Electromagnetic drivers or actuators forming a part of a wire print mechanism are energized to actuate each wire as needed to form the desired character. The actuators generally comprise an electromagnet solenoid, for example, having its armature fastened to an associated wire, the energization of which produces longitudinal movement of the wire in its guide. Such a wire print mechanism is disclosed in U.S. Pat. No. 3,627,096, which is assigned to the same assignee as the present invention.
The principle limitation of this type of wire print mechanism is the maximum repetition rate at which the print wire can be fired at the paper in a controlled way. The maximum acceleration of the wire is limited by the ratio of the applied force to the mass of the moving parts. This ratio is bounded in that there is a limit to the energy that can be imparted to such an assembly by the magnetic circuit without generating an unacceptable increase in heat or causing the occurrence of physical distortion. In addition, the wire, after having been fired, bounces off the platen and returns to its original location retaining a significant proportion of the energy imparted to it. This energy must be dissipated and the wire brought to rest before it can be fired again, or resonant conditions may be set up. The problem is alleviated to some extent by the use of return springs and mechanical dampers. Finally, the build-up of current in the energizing winding is delayed by the inductance of the winding and a further limitation on speed is imposed.